Originally posted by Iain McNeill I always thought that, given a particular speaker, the ported cabinet would always be smaller than the sealed cabinet for optimum LF response??

Rarely. Just depends on the driver. A Qts well above .40 often requires a large sealed cab. Very low Qts drivers (like under .2) often require tiny vented boxes, but those don't usually provide much low freq response anyway.

In the case of this Colossus 18, I'm guessing low freq response will be VERY limited in a sealed enclosure, and that boosting the low freq way up via EQ to overcome that probably wouldn't be a good idea for anything other than a personal application in a person's home, given that Xmax is probably limited to 5-10mm. However, an optimum vented cabinet for it will most likely be fairly large. A sealed cab would probably be very small, but not have any low freq output to speak of.. at least not without a lot of EQ, which will hinder max output substantially.

Rarely. Just depends on the driver. A Qts well above .40 often requires a large sealed cab. Very low Qts drivers (like under .2) often require tiny vented boxes, but those don't usually provide much low freq response anyway.

In the case of this Colossus 18, I'm guessing low freq response will be VERY limited in a sealed enclosure, and that boosting the low freq way up via EQ to overcome that probably wouldn't be a good idea for anything other than a personal application in a person's home, given that Xmax is probably limited to 5-10mm. However, an optimum vented cabinet for it will most likely be fairly large. A sealed cab would probably be very small, but not have any low freq output to speak of.. at least not without a lot of EQ, which will hinder max output substantially.

I want to use the speaker in a mobile disco environment so it needs to be as loud as possible.

Would a simple opening on the rear of the box allow in enough air to get sufficient bass ? Or would this pollute the sound from the front ?

Originally posted by nigelwright7557 There is no room at the front around the speaker for a port.
I suppose I could put one on the back of the box if it was kept simple.

Would a simple hole do the job or would it need a pipe ?

Doesn't work that way.
First of all, you need to figure out which Colossus 18 you have, as there are currently several (4 I think?), and there might have been even more in the past. Check this link here: http://www.fane-acoustics.com/proseries.asp

Once you figure out which one it is, you need to download the PDF and enter the TS specs in WinISD Pro or something similar to simulate an optimum enclosure.

If you're trying to put it in some sealed enclosure of an unknown size, there's a small chance it might work OK by selecting the right diameter and length of PVC pipe (or whatever) and making a corresponding hole in the cabinet. Chances are slim though. If it's an old sealed cab for a single 18", it's probably too small.